The present invention relates to closure devices, and in particular, relates to injection molded caps for containers which hold liquid, such as milk.
Injection molded caps for blow molded milk bottles have been used for many years. Generally, two types of caps are available, push-on caps and thread-on caps. Push-on caps are installed by aligning the cap with the opening of a container and simply applying an axial force to the top of the cap. Thread-on caps generally require that the cap and container be aligned and that a rotative force be applied to the cap. In some cases, threaded caps, if carefully designed in conjunction with the container to which it is applied, can be made so that the rotative force required to install the cap is minimized or even eliminated. These kinds of injection molded caps are often made with low density polypropylene, a common material used in injection molding.
One of the problems associated with injection molded caps relates to dimensional stability. Polypropylene and other injection moldable materials tend to shrink when they are cooled. The amount of shrinkage is difficult to quantify, and depends on factors such as temperature, the presence or absence of additives such as pigments, the configuration of the product, and other factors. Another aspect of dimensional stability relates to the deformability of the cap at the time it is ejected from the mold. When the cap is still warm after being formed in the mold, forces required to eject the cap can cause deformation of the cap. In some cases, this results in permanent changes in the shape of the product.
Another problem arising from the use of plastic caps and blow molded bottles relates to the seal which must be created between these two components. The imprecise nature of blow molding requires that cap designs be forgiving. Caps must be designed for a wide range of bottle neck shapes, since it is difficult to blow mold containers within tight tolerances.
The problem of matching a blow molded bottle neck with an injection molded cap manifests itself both with respect to the sealing of the two components and with respect to the formation of a tamper-evident connection between the two components. For example, plug-type caps have a downwardly depending plug formed on the underside of the cap. The plug is intended to seal against the inner edge of a lip formed at the top of a container. If the plug of the cap shrinks and the diameter of the container neck at the lip does not properly match the shrunken size of the plug, an effective seal may not be possible. Similarly, many threaded caps include a ratchet ring formed at the lower periphery of the cap. The ratchet ring engages matching ratchet teeth formed on a bottle neck. If the dimensional stability of the components is not sufficient, the tamper-evidency provided by the ratchet ring will not be accomplished.
A further problem arising from the use of plastic caps and blow-molded bottles relates to the automated installation of such caps onto the blow-molded bottles. The installation process involves the loose placement of a cap onto a container neck. Such loose placement occasionally results in a "cocked" cap, which in the next step of installation can result in improper engagement between the tightening tool and the cap or cross-threading of the threads of the cap and the container neck. In these instances, the capping operation can be disrupted, requiring the attention of an operator.
It is therefore an object of the present invention to provide a cap with improved dimensional stability.
Another object of the present invention is to provide a cap in which the effects of shrinkage are reduced.
Yet another object of the present invention is to provide a cap having improved sealing characteristics with respect to bottle containers which are manufactured to relatively loose tolerance requirements.
Still another object of the present invention is to provide an improved tamper-evident cap.
A further object of the present invention is to provide a tamper-evident threaded cap with an improved ratchet ring which prevents removal of the cap unless the ratchet ring has previously been removed.
A further object of the present invention is to provide a threaded cap which reduces the likelihood of disruptions in an automatic capping operation.
Another object of the present invention is to provide a cap for a threaded container in which the amount of rotation required to secure and remove the caps is reduced.
Yet another object of the present invention is to provide a cap which can be produced with less resin than other caps.
These and other objects of the present invention are achieved with a threaded cap which is comprised of a generally flat circular cover with a depending skirt extending from the periphery of the cover. At the bottom of the skirt, a ratchet ring is frangibly connected to the skirt. The ratchet ring includes a plurality of inwardly directed ratchet teeth. The underside of the cover includes various formations which tend to resist deformation of the cap which tends to occur as a result of shrinkage of the material comprising the cap. The cap includes a sealing plug and an auxiliary sealing ring disposed at the outside base of the sealing plug. The auxiliary sealing ring creates a seal against the top surface of a container neck, and will create a seal even if the sealing plug does not fit tightly against the inside edge of the container neck. The ratchet teeth on the tamper-evident ratchet ring are shaped to enhance the locking action of the teeth. The abutting face of each tooth is sloped so that the bottom edge of the tooth is offset with respect to the upper part of the tooth in the direction of unscrewing the cap.
In an alternative embodiment of the invention, the threads of the cap are generally disposed on the upper portion of the inside surface of the skirt of the cap. This creates an unthreaded section on the lower portion of the inside surface of the cap which assists in alignment of the cap and reduces the tendency of the caps to assume an improper position prior to being tightened. In the alternative embodiment, the cap has a thread configuration comprising four thread segments, each of which occupies a discrete circumferential section of the inside surface of the cap. The beginning of one thread is separated from the end of the adjacent thread by about 5 degrees. The separation of the thread segments creates vertically unthreaded areas which allow for circumferential expansion of the cap to accommodate variation in the relative size of the cap and various container necks.